While natural gas has become an economically attractive commodity, liquefaction and regasification are remarkably energy intensive processes. In many instances, liquefaction of natural gas requires about 230 kW for each MMscfd of high-pressure natural gas, which corresponds to about 280 MW of power in a 1,200 MMscfd liquefaction plant. On the other hand, regasification of 1,200 MMscfd LNG requires about 750 MM Btu/hr of heating duty.
Most typically, heating duty is supplied by heat exchange with seawater cooling about 100,000 gpm of seawater by 15° F., or using combustion heat from 20 MMscfd of fuel gas, which is equivalent to about 1.5% of the import LNG. Unfortunately, the ecologic impact in either scenario, and especially over prolonged periods is significant. Thus, most conventional LNG regasification processes are energy inefficient or often environmentally problematic. At least theoretically, some of the power consumed in LNG liquefaction may be recoverable at the LNG receiving terminal if the LNG is used as a refrigerant in processing facilities or as a heat sink in power generation. Indeed, there are potentially significant synergies between power generation and LNG regasification. For example, waste heat from gas turbine exhaust is readily available as a heat source for LNG regasification. Similarly, integration with a processing facility such as a refinery or chemical plant may be especially beneficial as the waste heat from these facilities can be used for regasifying LNG.
Among other known configurations and methods, Mandrin and Griepentrog describe in U.S. Pat. Nos. 4,036,028 and 4,231,226, respectively, integration of a power plant with LNG regasification. Similar plant configurations are reported in published U.S. Pat. App. No. 2003/0005698 to Keller, EP 0 683 847 to Johnson et al., and WO 02/097252 to Keller. In such known configurations, heat for regasification of LNG is typically provided by a heat exchange fluid, which is in thermal exchange with a gas turbine intake air or flue gas exhaust. These configurations improve the efficiency of the gas turbine cycle by densifying the inlet air, thereby increasing its power output and efficiency. However, such LNG regasification processes rely on the heat content in the gas turbine intake air for LNG heating that may not be available during winter months, especially in colder climates. Therefore, additional heating with conventional methods is often necessary.
Thus, while all or almost all of such improved configurations and methods provide at least some advantages over previously known configurations, various disadvantages still remain. Among other things, most of the known methods fail to provide continuous sources of heating for LNG regasification, and therefore rely on supplementary heating. Therefore, there is still a need for improved plant configurations and methods of thermal integration of LNG regasification.